Disallow TextArea resize if cols is specified

[metonym]

A recent fix to the upstream Carbon library caught my eye: carbon-design-system/carbon#13069

It disables the "resize" attribute for TextArea if the cols prop is specified.

The differences in behavior compared to the Svelte implementation:

• cols does not have a default value (the Svelte implementation defaults to 50)
• if cols is not specified, the textarea has width=100%
• if cols is specified, the textarea unsets width and applies the style rule resize=none

If we want to align with the upstream library, this would be a breaking change:

- export let cols = 50;
+ export let cols = undefined;

+ <textarea style:resize={typeof cols === "number" ? "none" : undefined} />

[theetrain]

Perhaps we can include this change as part of the v11 upgrade, assuming the flagship library adopted this behaviour in v11.